Conventionally, in a hybrid vehicle mounted with an internal combustion engine and a motor as running power sources, drive control has been performed by switching between two or more motor control modes including, for example, a sinusoidal Pulse Width Modulation (PWM) control mode, an overmodulation PWM control mode, and a rectangular wave control mode.
For example, JP 2007-306658 A (hereinafter referred to as “Patent Literature 1”) discloses a motor drive system in which a DC voltage supplied from a battery is boosted by a boost converter and input to an inverter which converts the DC voltage to an AC voltage and applies the AC voltage to a motor for driving the motor. In this motor drive system, a motor control mode can be switched from a sinusoidal PWM control mode to a rectangular wave control mode for the same operation point of the motor by lowering a boost voltage boosted by a boost converter. As a result, system efficiency can be improved, further resulting in improved fuel efficiency of a vehicle.